Mercaptan-containing polymers having at least two terminal (i.e., reactive) mercaptan groups can be easily cured at room temperature to produce elastomers having excellent properties, such as for example, resistance to weathering, oil, ozone, and water which makes these suitable for a variety of uses. Because such polymers are easily cured and are resistant to the elements they have been widely used as sealants and adhesives, as well as in many other applications. These mercaptan-containing polymers, however, have generally had the disadvantage that a "curing agent" had to be added to the polymers just prior to their use.
When a sealant composition comprising at least two components must be mixed just prior to use, such a sealant composition is normally called a "two-package" sealant system; whereas, a sealant composition that can be premixed and stored without a substantial amount of curing for a reasonable period of time and thus is sold "ready to use" is called a "one-package" sealant system. A one-package sealant composition must be capable of remaining relatively uncured in a container for an extended period of time, for example about six months, and then begin to cure after and only after being exposed to environmental conditions, such as air, water, or light.
Two-package systems are often used as standards against which one-package systems are compared because two-package systems have been in use for a long period of time (and are thus well established) and because they generally have better performance properties than one-component systems. However, one-package systems are generally preferred systems since they can be applied directly from a container without any necessity of mixing at the time of application and thus avoid the potential problem of improper mixing of the components. Several attempts have been made to develop one-package systems that contain both the sealant base and the curing agent and which are activated only when exposed to normal environmental conditions. An example of a one-package system is disclosed in U.S. Pat. No. 3,225,017, wherein a mercaptan-terminated polysulfide-based composition is cured by exposure to moisture. That system requires much moisture to cure and, therefore, is not useful in relatively arid climates.
Another one-package system is disclosed in U.S. Pat. No. 3,991,039, wherein a mercaptan-containing polysulfide polymer-based composition is cured by exposure to air or oxygen. In that patent, a curing package comprising a combination of a thiuram disulfide and an iron or manganese complex is disclosed. However, that curing package does not effectively cure all types of mercaptan-containing polymers; and, in particular, it does not effectively cure certain mercaptan-containing polymers which contain mostly monosulfide linkages with minor amounts of disulfide and polysulfide linkages (and which are disclosed in U.S. Pat. No. 3,817,936 and in recently allowed application having Ser. No. 737,948 now U.S. Pat. No. 4,113,707) such polymers generally remaining tacky for long periods of time when the above-described curing package is mixed with them.
A curing package has now been found which effectively cures even mercaptan-containing polymers with mostly monosulfide linkages. The compositions become tack-free to polyethylene film within a relatively short period of time and have good resilience.
It is an object of this invention to produce air-curable compositions which can be used to prepare "one-package" sealants.
It is a further object of this invention to produce air-cured sealant compositions which cure rapidly.